The present invention relates to comminuting or shredding machines in general, and more particularly to improvements in machines for cutting or shredding tobacco or analogous fibrous materials. Still more particularly, the invention relates to improvements in machines for cutting tobacco or the like wherein two convergent conveyors convert a stream of fibrous material into a continuous cake which is caused to move lengthwise and whose leader is severed by one or more orbiting knives so that the cake yields particles in the form of shreds or the like.
The term "tobacco" is intended to embrace natural tobacco (including leaves, tobacco leaf laminae and/or ribs), reconstituted tobacco as well as tobacco substitutes. As a rule, such material is fed into an upright duct at the rear end of a conveyor system which serves to convert the particles into a cake and delivers the leader of the cake into the range of one or more driven knives. The supply of tobacco which descends in the duct is accepted by the rear portion of the upper reach of an endless chain or belt conveyor which constitutes one component of the aforementioned conveyor system and cooperates with the lower reach of a second chain or belt conveyor to gradually compact the fibrous material while simultaneously transporting the resulting cake toward and through a mouthpiece which is installed immediately in front of the severing or shredding station. In order to ensure continuous descent of fibrous material in the duct, the latter comprises or confines a mobile rear wall which is oscillated or performs analogous recurrent movements so as to prevent bridging of particles in the duct before the particles reach and are entrained by the conveyor system. The latter defines a substantially or nearly horizontal forwardly converging path for the cake.
It is desirable and advantageous to subject the particles of fibrous material in the region of the conveyor system to a constant and predictable compacting action. Such treatment guarantees the formation of satisfactory shreds and prolongs the useful life of the knife or knives at the shredding station. Constant and predictable compacting action depends, at least to a certain extent, on the height of the supply of fibrous material in the duct. Thus, if the height of the supply is constant, and if the consistency of material in the duct is also constant, the machine is much more likely to produce a cake of predictable characteristics.
In most tobacco cutting machines, the rear wall of the duct behind the path which is defined by the conveyor system simply pivots back and forth about a fixed axis. Reference may be had, for example, to U.S. Pat. No. 2,275,103. It has been found that a rear wall which is mounted and moves in the just described manner is incapable of invariably preventing the development of voids in the supply of fibrous material in the interior of the duct and/or in the tobacco cake. Moreover, such rear wall cannot always prevent or reduce the probability of or eliminate bridging of fibrous material in the duct. The likelihood of unsatisfactory progress of fibrous material toward the severing station is especially pronounced in the critical region where the direction of travel of particles is changed from vertical to horizontal, i.e., in the region of the lower end of the duct at the rear end of the aforementioned path. Cavities in the cake of fibrous material between the conveyors of the conveyor system necessarily entail the development of zones wherein the density of the cake is less than the desired optimum density. This, in turn, exerts a highly undesirable influence upon the quality of shreds as well as on the useful life of the severing instrumentalities.